This is an application requesting funding for Years 36-40 of a long-standing, highly successful Institutional Training Grant that supports postdoctoral research training in transfusion medicine and benign hematology. Since the last competitive renewal in 2007, funded research at the BloodCenter of Wisconsin (BCW) has continued to increase, and faculty available to mentor fellows has increased to 32. Available research space has been roughly doubled by an addition to the Blood Research Institute that was completed in December 2006. An agreement has been negotiated with the Medical College of Wisconsin (MCW) under which BloodCenter physicians now constitute the Section of Benign Hematology in the Division of Hematology-Oncology. Together, these developments enhance basic research training opportunities, open new avenues for clinical/translational research, and provide training grant faculty with unprecedented access to residents and fellows who have an interest in research training. Research opportunities available to trainees cover a broad range of clinical and basic research subjects relevant to transfusion medicine and hematology, including Immunology, Vascular Biology/Hemostasis, Transfusion Medicine, Stem Cell Biology, and Clinical Research. The research training experience will be essentially full time. Trainees will be expected to gain a basic understanding of the disciplines in which they undertake their investigations, develop competency with a variety of research technologies, strengthen their grasp of their chosen research by taking selected courses in the graduate studies program of MCW, and develop the ability to conduct independent research. Time spent in fellowship training is regarded as one of several stages of professional development. Accordingly, additional tracks will be offered to selected trainees, including the opportunity 1) to apply for a Clinical Investigator Development Award (K08) for continued mentoring, 2) to apply for independent grant support, and 3) for those oriented toward a career in transfusion medicine, an opportunity for further training as a junior member of BloodCenter's medical staff. Ultimately, trainees are expected to pursue academic or alternate careers in transfusion medicine, hematology, or closely related fields.